EP4110989B1 - Device and method for producing a pulp web - Google Patents

Description

The invention relates to a method for producing a fibrous web, in particular a tissue web or hygiene paper web, with a first press dewatering of the fibrous web, the fibrous web being in a first pressing area between a first covering, the first covering being a felt, and a rotating press jacket with line forces between 80 kN/m to 600 kN/m is pressed and the fibrous web is transferred to the rotating press jacket, with a guidance of the fibrous web directly on the press jacket from the first pressing area to a first transfer area, with a transfer of the fibrous web in the first transfer area from which rotating press jacket on a transfer clothing and a transfer of the fibrous web in a second transfer area from the transfer clothing to a drying cylinder. The invention also relates to a device for producing a fibrous web, as specified in the preamble of claim 6.

In general, to produce a fibrous web, in particular a tissue web or sanitary paper web, a fibrous suspension is introduced via a headbox between two coverings and dewatered centrifugally. The Crescent Former concept is used particularly in the area of tissue production, i.e. the fibrous suspension is introduced between a felt and a forming fabric, with the fibrous web being formed by dewatering the fibrous suspension. After the formation of the fibrous web, the forming fabric is lifted off the fibrous web, with the fibrous web lying on the felt being fed to the further process steps, including further mechanical and / or thermal dewatering and rolling up to the end product.

In the AT 508 331 A1 discloses a method and apparatus for treating a fibrous web in a Langnip press unit. A method for tissue production is provided in which the dewatering and transport of the fibrous web is carried out in a simple and compact press arrangement.

The DE 2805494 A1 refers to the pressing part of a wet web former for pulp or the like, which consists of at least two consecutive pressing points, a preheater being arranged between the pressing points and the preheater operating in such a way that evaporation of the water from the pulp web does not take place to a significant extent.

The WO2017139125A1 discloses a "molding roll" for producing paper products, with a cylindrical jacket, with a vacuum box being arranged within the cylindrical jacket. 3 shows a paper machine with belt creping, the paper web being dewatered in a shoe press and, after belt creping, being passed over a vacuum box, the vacuum increasing the caliper of the paper web by sucking the paper web into it the topography of the creping belt allows. Furthermore, a paper machine is disclosed in Figure 5, wherein the paper web is fed to a molding nip on a transfer fabric and further fed to a transfer nip via the molding roll.

The US2002088577A1 discloses impingement drying for producing an absorbent fibrous web and particularly relates to a method for producing a non-compressively dewatered absorbent sheet which is dried by impingement drying.

The WO9713031A1 discloses a method in a paper machine, wherein a web is dewatered in at least one press nip and subsequently dried in a drying group.

The aim of the invention is to produce a fibrous web with improved quality properties while maintaining low energy consumption, low operating costs and low investment costs.

This is achieved according to the invention by thermally drying the fibrous web between the first transfer area and the second transfer area. According to the invention, the fibrous web is pressed in the first pressing area at line forces between 80 kN/m and 600 kN/m, with the fibrous web being pressed directly between the first covering, a felt, and a rotating press jacket. The fibrous web is transferred from the first covering to the rotating press jacket in the first pressing area and then directly onto it the press jacket - from the first pressing area to a first transfer area. In the first transfer area, the fibrous web is transferred from the rotating press jacket to a transfer clothing. According to the invention, an improvement in the quality properties of the fibrous web is achieved in this first transfer area when the fibrous web is transferred to the transfer clothing, with a deterioration in the quality properties again occurring when the fibrous web is transferred in the second transfer area from the transfer clothing to the drying cylinder. This deterioration results from the existing compression of the fibrous web when it is transferred from the transfer clothing to the drying cylinder. Surprisingly, it was recognized that with a further increase in the dry content of the fibrous web through thermal dewatering between the first transfer area and the second transfer area, a better preservation of the quality properties of the fibrous web in the second transfer area is possible, whereby overall improved quality properties of the fibrous web can be achieved. The dry content of the fibrous web after the first transfer area is typically between 35% and 50%, with the dry content being defined as the quotient of the mass of dry fiber and the sum of the mass of dry fiber and mass of water. By thermally drying the fibrous web between the first transfer area and the second transfer area, the dry content of the fibrous web in the second transfer area is increased by 3% to 10%, whereby the percentages are again to be understood as percent dry content in accordance with the definition above. For example, with a dry content of the fibrous web of 42%, an increase in the dry content of the fibrous web of approximately 1% (to 43%) is possible through further thermal drying between the first transfer area and the second transfer area if the drying of the fibrous web is over a length of 1 meter in the machine direction. A linear scalability of drying over the drying length is obvious in this dry content range.

A favorable embodiment of the invention is characterized in that the fibrous web is structured in the first transfer area, the structuring of the fibrous web taking place by transferring the fibrous web from the faster rotating rotating press jacket to the slower rotating transfer clothing and the transfer clothing being structured Transfer covering is carried out. This is advantageous because the structuring of the fibrous web in the first transfer area results in an improvement in the quality properties of the fibrous web, with the transfer of the fibrous web from the faster rotating rotating press jacket to the slower rotating structured transfer covering resulting in an improvement, ie an increase, in the fibrous web thickness or .of the bulk [cm ³ /g], which is defined as the ratio of leaf thickness [mm] to leaf weight [g/m ² ], and an improvement in water absorption in terms of water absorption capacity is achieved. Structured transfer coverings include coverings that are typically used on TAD (Through Air Dryer) machines / through-flow drying machines for through-flow drying of the tissue web or sanitary paper web and therefore in particular TAD drying screens.

A further favorable embodiment of the invention is characterized in that the thermal drying of the fibrous web guided on the transfer covering comprises convection drying of the fibrous web, with drying air being applied directly to the fibrous web via a drying device and the drying air being sucked back into the drying device. The fibrous web guided on the transfer covering after the first transfer area is advantageously first dried by convection drying, for example impingement drying. Since the fibrous web after the first transfer region has a lower initial permeability corresponding to the dry content, ie permeability for the drying air, convection drying is advantageous because hardly or only a small part of the drying air flows through the fibrous web guided on the transfer covering. The drying air from the drying device is therefore applied directly to the fibrous web, whereby when the drying air hits the fibrous web, the drying air is deflected and the water evaporated from the fibrous web is absorbed into the drying air. The drying air is then sucked back into the drying device. The drying device is typically designed as a drying hood or as an impingement flow drying hood, with the drying air typically being applied directly to the fibrous web via slot or hole nozzles. The drying air is blown out at a temperature between 100°C and 150°C and a blow-out speed between 60 m/s and 100 m/s Drying hood applied directly to the fibrous web. The maximum temperature of the drying air is limited to 240°C. This limitation results from the heat resistance of the usual structured transfer coverings. Heat resistance of the structured transfer coverings would be achieved by choosing special plastics, even at higher temperatures, but it would hardly be economical.

A further favorable embodiment of the invention is characterized in that the thermal drying of the fibrous web guided on the transfer covering further comprises through-flow drying of the fibrous web, the drying air being applied directly to the fibrous web via the drying device, and a first part of the drying air being sucked back into the drying device is and a second part of the drying air is sucked through the fibrous web into a suction device, the transfer covering being guided between the fibrous web and the suction device. After a first convection drying of the fibrous web, there is typically an improvement in the permeability, ie the permeability of the fibrous web for the drying air, and thus better conditions for through-flow drying of the fibrous web. In the area of through-flow drying, the drying air from the drying device is applied directly to the fibrous web. When the drying air hits the fibrous web, a first part of the drying air is deflected, the water evaporated from the fibrous web is absorbed into the drying air and then this first part of the drying air is sucked back into the drying device. A second part of the drying air is sucked through the fibrous web into a suction device, the fibrous web being dried as the drying air flows through it. A suction device can be designed, for example, as a vacuum box or suction box or as a vacuum roller. For guidance - the first part of the drying air typically comprises two thirds or more of the applied drying air and the second part of the drying air comprises up to one third of the applied drying air. The drying device can comprise separate drying devices for convective drying and flow drying, or can be designed as a drying device for both convection drying and flow drying. Again the drying air is provided with a Temperature between 100°C and 150°C and a blow-out speed between 60 m/s and 100 m/s from the drying hood directly onto the fibrous web.

An advantageous embodiment of the invention is characterized in that for thermal drying of the fibrous web between the first transfer area and the second transfer area, drying air is applied directly to the fibrous web, the temperature of the drying air being adjusted by direct and/or indirect use of process waste heat and the Process waste heat occurs during the thermal drying of the fibrous web after the second transfer area and / or in secondary systems, in particular in a vacuum system. Advantageously, the energy efficiency of the entire system is improved because process waste heat can be used. At the same time, the increase in the dry content of the fibrous web between the first transfer area and the second transfer area improves the quality properties of the fibrous web, which is not to be expected since improvements in the quality properties are often accompanied by a deterioration in the energy efficiency of the entire system. Process waste heat from the thermal drying of the fibrous web after the second transfer area and/or from secondary systems, in particular from a vacuum system, can be used as usable process waste heat. Examples of thermal drying after the second transfer area include drying the fibrous web on a drying cylinder (for example a Yankee dryer, ie a drying cylinder with a diameter of 1800 mm to 6000 mm), or high-temperature hood drying, where the high-temperature drying hood is assigned to the drying cylinder and enables high-temperature convection drying of the fibrous web guided on the drying cylinder. High-temperature convection drying refers to drying with drying air with a temperature above 280°C and typically in a range between 350°C to 500°C, although temperatures up to 650°C can also be used. The waste heat from high-temperature hood drying has a lower temperature level, with the temperature of the waste heat being at least above 200 ° C and typically above 250 ° C. Reducing the temperature of the waste heat is possible simply by mixing it with cold ambient air or cooler process air. Drying the fibrous web on a drying cylinder - for example a Yankee dryer - also involves a steam and condensate system, with the drying cylinder being heated with the steam from the steam and condensate system. The condensate produced in the steam and condensate system is available at a pressure level above atmospheric and can be used directly by pressure relief, ie throttling, of the condensate to a lower pressure level, whereby the condensate is partially evaporated and the steam obtained in this way is added to the drying air can be. A direct removal of steam from the steam and condensate system for addition to the drying air is also conceivable. The waste heat from secondary systems, in particular from a vacuum system, can also be used. When using vacuum blowers to create a vacuum, exhaust air from the vacuum system is hot at up to 150°C. Direct use of this process waste heat from the vacuum system to dry the fibrous web in the area between the first transfer area and the second transfer area is advantageous. In general, the process waste heat can be used directly and/or indirectly to adjust the temperature of the drying air, whereby with direct use, waste heat or waste heat air is used directly as drying air and with indirect use, waste heat is used indirectly to heat the drying air. Typically, indirect heating involves the use of heat exchangers to transfer the waste heat to the drying air. Furthermore, cooler process air or ambient air can be used to set a desired drying air temperature or to reduce a drying air temperature that is too high.

The invention also relates to a device for drying a fibrous web, in particular a tissue web or sanitary paper web, according to claim 6, wherein a drying device for thermally drying the fibrous web is arranged in the area between the first transfer area and the second transfer area. According to the invention, a better preservation of the quality properties of the fibrous web in the second transfer area is possible, as a result of which overall improved quality properties of the fibrous web can be achieved.

An equally advantageous embodiment of the device is characterized in that the drying device is located between the first transfer area and the second transfer area comprises a convection drying area, via the drying device drying air can be applied directly to the fibrous web, wherein in the convection drying area the drying air can be sucked back into the drying device. Advantageously, the drying device further comprises a flow drying area, wherein drying air can be applied directly to the fibrous web via the drying device, a suction device is arranged in the flow drying area opposite the drying device and at least part of the drying air can be sucked into the suction device. In the through-flow drying area, the transfer clothing is guided between the drying device and the suction device, with the drying air from the drying device being able to be applied directly to the fibrous web. The drying device is typically designed as a drying hood or as an impingement flow drying hood, whereby the drying air can be applied directly to the fibrous web via slot or hole nozzles. A suction device can be designed, for example, as a vacuum box or suction box or as a vacuum roller. In the case of the vacuum roll, the transfer clothing can be suctioned in the area where the vacuum roll is wrapped. By applying the drying air to the fibrous web, the impulse of the drying air acts on the transfer clothing, which creates a force effect on the transfer clothing in the flow direction of the applied drying air. The effect of force on the transfer clothing causes the transfer clothing to bend in the direction of flow of the applied drying air. It is therefore advantageous to implement clothing-stabilizing elements in the area of the suction device, which limit deflection of the transfer clothing. Guide rollers can serve as clothing-stabilizing elements, with the guide rollers being designed on the side of the suction device and the transfer clothing being guided directly over the guide rollers. Depending on the distance between the guide rollers, the transfer clothing is also supported at this distance and deflection of the transfer clothing is limited. In particular, the suction device can be arranged between the clothing-stabilizing elements, for example suction boxes can be arranged between the guide rollers.

A further favorable embodiment of the device is characterized in that the drying device is connected directly or indirectly to a process waste heat line for the use of process waste heat that is generated during the thermal drying of the fibrous web after the second transfer area and / or in secondary systems, in particular in a vacuum system. Such a process waste heat line can, for example, be assigned to a process comprising the thermal drying of the fibrous web after the second transfer area and / or a secondary system, in particular the vacuum system. The waste heat or exhaust air from high-temperature hood drying has a temperature level of over 200°C and typically over 250°C. The waste heat from a vacuum system, especially when using vacuum blowers to create vacuum, delivers hot exhaust air of up to 150°C. In general, the process waste heat can be used directly and/or indirectly to adjust the temperature of the drying air.

• Fig. 1 zeigt eine Anlage zur Herstellung einer Faserstoffbahn entsprechend dem Stand der Technik.
• Fig. 2 zeigt eine erfindungsgemäße Vorrichtung zum Trocknen einer Faserstoffbahn.

The invention will now be described by way of example with reference to the drawings.

• Fig. 1 shows a system for producing a fibrous web according to the state of the art.
• Fig. 2 shows a device according to the invention for drying a fibrous web.

Fig. 1 shows a device for producing a fibrous web 1 according to the prior art, wherein to produce the fibrous web 1 a fibrous suspension is introduced via a headbox 14 between two coverings and centrifugally dewatered. The fiber suspension is introduced between a first covering 3, a felt, and a forming fabric and dewatered. After the formation of the fibrous web 1, the fibrous web 1 is guided on the first covering 3 to a first pressing area 2, where the fibrous web 1 is pressed between the first covering 3 and a rotating press jacket 4. The fibrous web 1 is transferred to the rotating press jacket 4 and guided directly on the press jacket 4 from the first pressing area 2 to a first transfer area 5, with a transfer of the fibrous web 1 in the first transfer area 5 from the rotating press jacket 4 to a transfer clothing 6, followed by a transfer of the fibrous web 1 in a second transfer area 7 from the transfer clothing 6 on a drying cylinder 8. After drying the fibrous web 1 on the drying cylinder 8, the fibrous web 1 is rolled up 15.

Fig. 2 shows a system for producing a fibrous web 1 with the device according to the invention for drying the fibrous web 1. After the formation of the fibrous web 1, the fibrous web 1 is guided on the first covering 3 to a first pressing area 2, where the fibrous web 1 is between the first covering 3 and a rotating press jacket 4 is pressed. The fibrous web 1 is transferred to the rotating press jacket 4 and guided directly on the press jacket 4 from the first pressing area 2 to a first transfer area 5, with a transfer of the fibrous web 1 in the first transfer area 5 from the rotating press jacket 4 to a transfer clothing 6. Advantageously, the fibrous web 1 is structured in the first transfer area 5, the structuring of the fibrous web 1 taking place by transferring the fibrous web 1 from the faster rotating press jacket 4 to the slower rotating transfer clothing 6 and the transfer clothing 6 being designed as a structured transfer clothing. According to the invention, thermal drying takes place after the first transfer area 5 and before a second transfer area 7, in which the fibrous web 1 is transferred from the transfer clothing 6 to a drying cylinder 8. For thermal drying of the fibrous web 1, drying air is applied directly to the fibrous web 1 via a drying device 9, the drying device 9 having a convection drying area 11. In the convection drying area 11, the drying air is applied directly to the fibrous web 1 and sucked back into the drying device 9. The drying device 9 further has a through-flow drying area 12, whereby the drying air is applied directly to the fibrous web 1 via the drying device 9, a first part of the drying air is sucked back into the drying device 9 after drying and a second part of the drying air is fed through the fibrous web a suction device 10 is sucked. In the area of the suction device 10, clothing-stabilizing elements 13 are advantageously implemented. The clothing-stabilizing elements 13 include guide rollers, with a design as a suction roller 17 also being possible. The drying air is used directly and/or indirectly from process exhaust air. For example, the exhaust air from the High-temperature drying hood 18 can be used as a supply air drying device 19.

The present invention therefore offers numerous advantages. It allows the production of a fibrous web with improved quality properties while maintaining low energy consumption and therefore low operating costs. Low investment costs are also possible because the drying cylinder for thermally drying the fibrous web after the second transfer area can be made smaller.

Reference symbols

(1)

fibrous web

(2)

first pressing area

(3)

first covering

(4)

rotating press jacket

(5)

first transfer area

(6)

Transfer covering

(7)

second transfer area

(8th)

Drying cylinder

(9)

Drying device

(10)

Suction device

(11)

Convection drying area

(12)

Flow drying area

(13)

tension-stabilizing element

(14)

Headbox

(15)

Roll up

(16)

High temperature drying hood

(17)

A tension-stabilizing element designed as a suction roller

(18)

Exhaust air high temperature drying hood

(19)

Supply air drying device

Claims (11)

1. Method for producing a pulp web (1), especially a tissue or sanitary paper web, with a first dewatering of the pulp web (1) by pressing, the pulp web (1) being pressed in a first pressing area (2) between a first clothing (3), the first clothing (3) being a felt, and a rotating press belt (4) with line loads between 80 kN/m and 600 kN/m, and the pulp web (1) being transferred to the rotating press belt (4), with the pulp web (1) being guided directly on the press belt (4) out of the first pressing area (2) to a first transfer area (5), with transfer of the pulp web (1) in the first transfer area (5) from the rotating press belt (4) to a transfer clothing (6) and transfer of the pulp web (1) in a second transfer area (7) from the transfer clothing (6) to a dryer (8), characterized in that the pulp web (1) is dried thermally between the first transfer area (5) and the second transfer area (7).
2. Method according to claim 1, where the pulp web (1) is structured in the first transfer area (5), where structuring of the pulp web (1) takes place by transferring the pulp web (1) from the rotating press belt (4), revolving at a higher speed, to the transfer clothing (6), revolving at a lower speed, and the transfer clothing (6) being designed as a structured transfer clothing.
3. Method according to claim 1, where thermal drying of the pulp web (1) on the transfer clothing (6) comprises convection drying of the pulp web (1), drying air being applied directly to the pulp web (1) by a drying device (9) and the drying air then being sucked back into the drying device (9) again.
4. Method according to claim 3, where thermal drying of the pulp web (1) carried on the transfer clothing (6) also comprises through-air drying of the pulp web (1), the drying air being applied through the drying device (9) directly to the pulp web (1), a first part of the drying air being sucked back into the drying device (9) again and a second part of the drying air being sucked through the pulp web (1) into a suction device (10), the transfer clothing (6) running between the pulp web (1) and the suction device (10).
5. Method according to claim 1, where drying air is applied directly to the pulp web (1) for thermal drying of the pulp web (1) between the first transfer area (5) and the second transfer area (7), the temperature of the drying air being set by direct and/or indirect use of process waste heat and the process waste heat being produced in thermal drying of the pulp web (1) after the second transfer area (7) and/or in sub-systems, particularly in a vacuum system.
6. Device for producing a pulp web (1), especially a tissue or sanitary paper web, with a first pressing area (2) for dewatering the pulp web (1) between a first clothing (3) designed as a felt and a rotating press belt (4), with line loads between 80 kN/m and 600 kN/m, with a first transfer area (5) for transferring the pulp web (1) from the rotating press belt (4) to a transfer clothing (6), the pulp web (1) being guided directly on the rotating press belt (4) between the first pressing area (2) and the first transfer area (5), and with a second transfer area (7) for transferring the pulp web (1) from the transfer clothing (6) to a dryer (8), where a drying device (9) for thermal drying of the pulp web (1) is disposed in the area between the first transfer area (5) and the second transfer area (7).
7. Device according to claim 6, where the transfer clothing (6) is designed as a structured transfer clothing (6) in the first transfer area (5), the speed of the structured transfer clothing (6) being slower than the circumferential speed of the rotating press belt (4) in the first transfer area (5).
8. Device according to claim 6, where the drying device (9) between the first transfer area (5) and the second transfer area (7) comprises a convection drying area (11) and drying air can be applied directly to the pulp web (1) by the drying device (9), where the drying air can be sucked back into the drying device (9) in the convection drying area (11).
9. Device according to claim 8, where the drying device (9) also comprises a through-air drying area (12), where the drying air can be applied directly to the pulp web (1) by the drying device (9), a suction device (10) being disposed opposite the drying device (9) in the through-air drying area (12) and where at least some of the drying air can be sucked into the suction device (10).
10. Device according to claim 9, where clothing stabilizing elements (13) are included in the area of the suction device (10), the clothing stabilizing elements (13) being disposed on the side of the suction device (10) and the transfer clothing (6) being guided between the drying device (9) and the clothing stabilizing elements (13).
11. Device according to claim 6, where the drying device (9) is connected directly or indirectly to a process waste heat duct in order to make use of process waste heat produced during thermal drying of the pulp web (1) after the second transfer area (7) and/or in sub-systems, especially in a vacuum system.

Images